Camouflage
Ibex are almost invisible in the Israeli desert.]] Camouflage, also known as cryptic coloration or concealing coloration, allows an otherwise visible organism or object to remain indiscernible from the surrounding environment. Examples include a tiger's stripes and the battledress of a modern soldier. Camouflage is a form of deception. The word camouflage comes from the French word camoufler meaning "to disguise." Natural camouflage with algae all over its body at Moss Beach, California]] In nature, there is a strong evolutionary pressure for animals to blend into their environment or conceal their shape; for prey animals to avoid predators and for predators to be able to sneak up on prey. Natural camouflage is one method that animals use to meet these. There are a number of methods of doing so. One is for the animal to blend in with its surroundings, while another is for the animal to disguise itself as something uninteresting or something dangerous. There is a permanent co-evolution of the sensory abilities of animals for whom it is beneficial to be able to detect the camouflaged animal, and the cryptic characteristics of the concealing species. Different aspects of crypsis and sensory abilities may be more or less pronounced in given predator-prey pairs of species. Some cryptic animals also simulate natural movement, e.g., of a leaf in the wind. This is called procryptic behaviour or habit. Other animals attach or attract natural materials to their body for concealment. A few animals have chromatic response, changing color in changing environments, either seasonally (ermine, snowshoe hare) or far more rapidly with chromatophores in their integument (chameleon, the cephalopod family). Some animals, notably in aquatic environments, also take steps to camouflage the odours they create that may attract predators. Some herd animals adopt a similar pattern to make it difficult to distinguish a single animal. Examples include stripes on zebras and the reflective scales on fish. Countershading (or obliterative camouflage), the use of different colors on upper and lower surfaces in graduating tones from a light belly to a darker back, is common in the sea and on land. This is sometimes called Thayer's law, after Abbott H. Thayer who published a paper on the form in 1896. Cryptic coloration s at Fuji]] This is the most common form of camouflage, found to some extent in the majority of species. The simplest way is for an animal to be of a color similar to its surroundings. Examples include the "earth tones" of deer, squirrels, or moles (to match trees or dirt), or the combination of blue skin and white underbelly of sharks (which makes them difficult to detect from both above and below). More complex patterns can be seen in animals such as flounder, moths, and frogs, among many others. Some forms of camouflage use contrasting shades to break up the visual outline, as on a gull or zebra. The type of camouflage a species will develop depends on several factors: *The environment in which it lives. This is usually the most important factor. *The physiology and behavior of an animal. Animals with fur need different camouflage than those with feathers or scales. Likewise, animals who live in groups use different camouflage techniques than those that are solitary. *If the animal is preyed upon, then the behavior or characteristics of its predator can influence how the camouflage develops. For example, if the predator is color blind, then the animal will not need to match the color of its surroundings. Animals produce colors in two ways: *Biochromes — natural microscopic pigments that absorb certain wavelengths of light and reflect others, creating a visible color that is targeted towards its primary predator. *Microscopic physical structures, which act like prisms to reflect and scatter light to produce a color that is different from the skin, such as the translucent fur of the Polar Bear, which actually has black skin. Camouflage coloration can change as well. This can be due to just a changing of the seasons, or it can be in response to more rapid environmental changes. For example, the Arctic fox has a white coat in winter, and a brown coat in summer. Mammals and birds require a new fur coat and new set of feathers respectively, but some animals, such as cuttlefish, have deeper-level pigment cells, called chromatophores, that they can control. Other animals such as certain fish species or the nudibranch can actually change their skin coloration by changing their diet. However, the most well-known creature that changes color, the chameleon, usually does not do so for camouflage purposes, but instead to express its mood. Beyond colors, skin patterns are often helpful in camouflage as well. This can be seen in common domestic pets such as tabby cats, but striping overall in other animals such as tigers and zebras help them blend into their environment, the jungle and the grasslands respectively. The latter two provide an interesting example, as one's initial impression might be that their coloration does not match their surroundings at all, but tigers' prey are usually color blind to a certain extent such that they cannot tell the difference between orange and green, and zebras' main predators, lions, are color blind. In the case of zebras, the stripes also blend together so that a herd of zebras looks like one large mass, making it difficult for a lion to pick out any individual zebra. This same concept is used by many striped fish species as well. Among birds, the white "chinstraps" of Canada geese make a flock in tall grass appear more like sticks and less like birds' heads. Mimicry Mimicry describes a situation where one organism, the mimic, has evolved to share common outward characteristics with another organism, the model, through the selective action of a signal-receiver. The model is usually another species, or less commonly, the mimic's own species, including automimicry, where one part of the body bears superficial similarity to another. The signal-receiver is typically another intermediate organism, e.g the common predator of two species, but may actually be the model itself. As an interaction, mimicry is always advantageous to the mimic and harmful to the receiver, but may either increase or reduce the fitness of the model. The distinction between mimicry and camouflage is arbitrarily defined in that the model in camouflage is not another organism; the arbitrary nature of this distinction between the two phenomena can be seen by considering animals that resemble twigs, bark, leaves or flowers, in that they are often classified as camouflaged (a plant does constitute the "surroundings"), but sometimes classified as mimics (a plant is also an organism). The more general category that encompasses such examples, therefore, is crypsis. Though mimicry is most obvious to humans in visual mimics, they may also use olfactory (smell) or auditory signals, and more than one type of signal may be employed.Wickler, W. 1968. Mimicry in plants and animals. McGraw-Hill, New York Mimicry may involve morphology, behavior, and other properties. In any case, the signal always functions to deceive the receiver by providing misleading information. Mimicry differs from camouflage in which a species appears similar to its surroundings. In evolutionary biology terms, this phenomenon is a form of co-evolution involving an evolutionary arms race, and should not be confused with convergent evolution, which occurs when species come to resemble on another independently due to similar lifestyles. Mimics may have multiple models during different stages of their life cycle, or they may be polymorphic, with different individuals imitating different models. Models themselves may have more than one mimic, though frequency dependent selection favors mimicry where models outnumber hosts. Models tend to be relatively closely related organisms,Campbell, N. A. (1996) Biology (4th edition), Chapter 50. Benjamin Cummings, New York ISBN 0-8053-1957-3 but mimicry of vastly different species is also known. Most known mimics are insects, though other mimics including mammals are known. Military camouflage wearing desert MARPAT camouflage.]] Camouflage was not in wide use in early western civilisation based warfare. 19th century armies tended to use bright colors and bold, impressive designs. These were intended to daunt the enemy, attract recruits, foster unit cohesion, or allow easier identification of units in the fog of war. Smaller, irregular units of scouts in the 18th century were the first to adopt colors in drab shades of brown and green. Major armies retained their color until convinced otherwise. The British in India in 1857 were forced by casualties to dye their red tunics to neutral tones, initially a muddy tan called khaki (from the Urdu word for 'dusty'). White tropical uniforms were dyed by the simple expedient of soaking them in tea. This was only a temporary measure. It became standard in Indian service in the 1880s, but it was not until the Second Boer War that, in 1902, the uniforms of the entire British army were standardized on this dun tone for battledress. Other armies, such as the United States, Russia, Italy, and Germany followed suit either with khaki, or with other colors more suitable for their environments. See also *Active camouflage *Animal coloration *Aposematism *Dazzle camouflage *Everett Warner References * * *Roy R. Behrens - Art and Camouflage: An Annotated Bibliography * * * *Jon Latimer, Deception in War, London: John Murray, 2001. *Everett L. Warner, “The Science of Marine Camouflage Design” in Transactions of the Illuminating Engineering Society 14 (5) 1919, pp. 215-219. *Everett L. Warner, “Fooling the Iron Fish: The Inside Story of Marine Camouflage” in Everybody’s Magazine (November 1919), pp. 102-109. Notes External links *Roy R. Behrens, "The Thinking Eye: a Chronology of Camouflage" 2006 *"An informal study into camouflage" *Camoupedia Category:Military camouflage Category:Survival skills